1. Field of the Invention
The present invention relates to an optical sensor unit for measuring the current and the voltage of a high frequency transmitted over e.g., a coaxial cable.
2. Description of the Background Art
In a semiconductor manufacturing system, employing high frequency plasma, the fundamental and harmonics components of a high frequency of, e.g. 400 kHz or 13.56 MHz, supplied from a high frequency power supply on a coaxial cable to a vacuum processing chamber are calculated by harmonics measuring equipment to oversee the manufacturing process. In conventional harmonics measuring equipment, a sensor unit comprised of a high-frequency measuring circuit including inductors and capacitors electrically senses the current and the voltage of the high frequency applied to the vacuum processing chamber, and transmits signals representative of the current and the voltage thus sensed on shielded signal cables to a data processor system, which analyzes the waveform by fast Fourier transform (FFT) to determine the current, voltage and the phase difference of the fundamental and second to fifth harmonics components, as disclosed for example in the Japanese laid-open publication Nos. 52994/1994 and 2001-68459.
With the above-described harmonics measurement equipment, however, if the aforementioned sensor unit is introduced in the transmission line for transferring the high frequency supplied from the high frequency power source to the vacuum processing chamber, there may be occasions where the signal cables for taking out sensed signals, connected to the sensor unit, operate as antennas to render it difficult to establish matching between the high frequency power source and a plasma discharging device in the vacuum processing chamber. Moreover, although a common optical sensor for measuring the high frequency is disclosed in for example the Japanese laid-open publication No. 105919/1996, there lacks the disclosure of an optical sensor convenient for measuring the high frequency supplied from the high frequency power supply to the vacuum processing chamber.